Cellulose resin, material for molding, molded body and process for producing cellulose resin

ABSTRACT

A cellulose resin formed by substituting hydrogen atoms of hydroxy groups of a cellulose with a long-chain component being a linear saturated aliphatic acyl group having 14 or more carbon atoms and a short-chain component being an acyl group having 2 or 3 carbon atoms, in which a degree of substitution with the long-chain component (DS Lo ) and a degree of substitution with the short-chain component (DS Sh ) satisfy conditional expressions (1) and (2) shown below:
 
DS Lo +DS Sh ≥2.1  (1)
 
4≤DS Sh /DS Lo ≤12  (2).

This application is a National Stage of International Application No. PCT/JP2016/086653 filed Dec. 9, 2016, claiming priority based on Japanese Patent Application No. 2015-256792 filed Dec. 28, 2015, the entire content of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a cellulose resin, a molding material, a molded body and a process for producing the cellulose resin.

BACKGROUND ART

Bioplastic using a plant as a raw material can contribute to a countermeasure against petroleum depletion and global warming and has been started being used not only in common products such as packaging, containers and fibers but also in durable products such as electronics and automobiles.

However, general bioplastics, such as polylactic acid, polyhydroxyalkanoate and modified starch, all use starch materials, more precisely, edible parts, as raw materials. Accordingly, for fear of future food shortage, it has been desired to develop a novel bioplastic using a non-edible part as a raw material.

As a raw material of a non-edible part, cellulose which is a main component of wood and plant is representative, and various types of bioplastics using the cellulose have been already developed and commercialized.

However, since a step of chemically modifying cellulose to obtain a resin suitable for molding is complicated and laborious and much energy is required for production, manufacturing cost of a cellulose resin is high. In addition, mechanical characteristics and durability (heat resistance, water resistance, etc.) of a produced resin is not sufficient.

Cellulose is produced as pulp by chemically separating lignin and hemicellulose from wood, etc., with the help of a chemical agent. In contrast, cotton can be used as it is since it is virtually formed of cellulose. Such a cellulose, which is a high molecular weight compound formed by polymerization of 3-glucose, has a large number of hydroxy groups and thus has strong intermolecular force due to hydrogen bonds. Because of this, cellulose is hard and fragile, and has no thermoplasticity and a low solubility in a solvent except a special solvent. In addition, due to a large number of hydrophilic hydroxy groups, water absorbability is high and water resistance is low.

For improving such properties of a cellulose, various investigations have been made.

As a method for improving the properties of a cellulose, a method of substituting a hydrogen atom of a hydroxy group in a cellulose with a short-chain acyl group such as an acetyl group is known. According to this method, since the number of hydroxy groups can be reduced, the intermolecular force of a cellulose can be reduced. A further investigation has been made for producing a cellulose derivative having satisfactory thermoplasticity and water resistance by introducing a long-chain organic group having a larger number of carbon atoms in addition to a short-chain acyl group such as an acetyl group.

For example, Patent Literature 1 describes a cellulose acylate film produced from a solution obtained by dissolving a cellulose acylate in which the substitution degree of hydroxy groups of the cellulose satisfies predetermined conditions, and a polycarboxylic acid which has 22 or less carbon atoms and a carboxyl group having an acid dissociation index of 4.4 or less, in an organic solvent. The literature describes a case where cellulose triacetate was used as the cellulose acylate. Since such a film can be easily removed from a support after producing by casting and drying, the productivity thereof is excellent.

Additionally, Patent Literature 2 describes a cellulose derivative produced by substituting at least a part of hydrogen atoms of hydroxy groups of a cellulose with a short-chain acyl group (for example, an aliphatic acyl group having 2 to 4 carbon atoms) and a long-chain acyl group (for example, an aliphatic acyl group having 5 to 20 carbon atoms), and that the cellulose derivative has a low water absorption rate, satisfactory thermoplasticity, strength and fracture elongation and is suitable for molding process.

Patent Literature 3 describes a process for producing a cellulose derivative, including the steps of introducing a long-chain organic group having 5 or more carbon atoms and a short-chain organic group having 4 or less carbon atoms to a cellulose by reacting them in a solid-liquid heterogeneous system, and conducting solid-liquid separation to obtain the cellulose derivative.

Patent Literature 4 describes a cellulose derivative having cardanol introduced therein, and that the cellulose derivative was improved in thermoplasticity, mechanical characteristics and water resistance.

Patent Literature 5 describes a cellulose derivative having cardanol and abietic acid introduced therein, and that the cellulose derivative was improved in thermoplasticity, mechanical characteristics and water resistance.

Patent Literature 6 describes a process for producing a cellulose derivative including a first step of reacting a cellulose with a long-chain reactant for introducing a long-chain organic group having 5 or more carbon atoms in a solid-liquid heterogeneous system to form a cellulose derivative having the long-chain organic group introduced therein and remaining hydroxy groups which are a part of the hydroxy groups of the cellulose, in a swollen state, and performing solid-liquid separation to obtain an intermediate cellulose derivative; and a second step of reacting the intermediate cellulose derivative with a short-chain reactant for introducing a short-chain organic group having 4 or less carbon atoms to form a final cellulose derivative having the short-chain organic group introduced therein.

CITATION LIST Patent Literature

Patent Literature 1: JP2002-265639A

Patent Literature 2: JP2010-121121A

Patent Literature 3: WO2013/180278

Patent Literature 4: WO2011/043279

Patent Literature 5: WO2011/043280

Patent Literature 6: WO2015/060122

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide a cellulose resin having excellent mechanical characteristics and durability and low environmental load (the proportion of a plant-derived component is high) and a process for producing the cellulose resin.

Solution to Problem

According to an aspect of the present invention, there is provided a cellulose resin formed by substituting hydrogen atoms of hydroxy groups of a cellulose with a long-chain component being a linear saturated aliphatic acyl group having 14 or more carbon atoms and a short-chain component being an acyl group having 2 or 3 carbon atoms in which a degree of substitution with the long-chain component (DS_(Lo)) and a degree of substitution with the short-chain component (DS_(Sh)) satisfy conditional expressions (1) and (2) shown below: DS_(Lo)+DS_(Sh)≥2.1  (1) 4≤DS_(Sh)/DS_(Lo)≤12  (2).

According to another aspect of the present invention, there is provided a molding material comprising the aforementioned cellulose resin.

According to another aspect of the present invention, there is provided a molded body formed by using the aforementioned molding material.

According to another aspect of the present invention, there is provided a process for producing the aforementioned cellulose resin, comprising:

acylating hydroxy groups of a cellulose constituting pulp by reacting

the pulp dispersed in an organic solvent with

a short-chain reactant (short-chain acylating agent) selected from acetyl chloride, acetic anhydride, propionic anhydride and propionyl chloride, and

a long-chain reactant being an acid chloride of a long-chain fatty acid and having the long-chain component,

in the presence of an acid trapping component while warming; and

separating an acylated cellulose obtained in the acylating from the organic solvent.

Advantageous Effects of Invention

According to an exemplary embodiment, there can be provided a cellulose resin having excellent mechanical characteristics and durability and low environmental load (the proportion of a plant-derived component is high) and a process for producing the cellulose resin.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a ternary diagram showing individual compositions of cellulose resins according to Examples and Comparative Examples of the present invention and suitable ranges of the compositions.

DESCRIPTION OF EMBODIMENTS

A cellulose resin according to an exemplary embodiment is a cellulose derivative formed by substituting hydrogen atoms of hydroxyl groups of a cellulose with a long-chain component being a linear saturated aliphatic acyl group having 14 or more carbon atoms and a short-chain component being an acyl group having 2 or 3 carbon atoms.

It is preferable that the degree of substitution with the long-chain component (DS_(Lo)) and the degree of substitution with the short-chain component (DS_(Sh)) satisfy the following conditional expressions (1) and (2): DS_(Lo)+DS_(Sh)≥2.1  (1) 4≤DS_(Sh)/DS_(Lo)≤12  (2).

Such a cellulose resin has excellent mechanical characteristics and durability and low environmental load (the ratio of a plant-derived component is high). As the mechanical characteristics, for example, excellent bending strength, elastic modulus and impact resistance can be obtained. As the durability, for example, excellent heat resistance and water resistance can be obtained.

Thermoplasticity and water resistance can be enhanced by introduction of a long-chain component. Owing to the presence of a long-chain component and a short-chain component in a predetermined ratio, mechanical characteristics such as bending strength, elastic modulus and impact resistance can be enhanced.

The cellulose resin according to an exemplary embodiment can possess a reinforcing crystal structure due to a cellulose main-chain crystal. Since the cellulose resin has such a crystal structure, mechanical characteristics such as elastic modulus can be improved or, e.g., chemical resistance or surface hardness can be enhanced.

In the cellulose resin according to an exemplary embodiment, it is preferable that the average number of hydroxy groups per glucose unit is 0.9 or less, in view of, e.g., flowability, water resistance and impact resistance.

(Cellulose)

Cellulose is a straight-chain polymer obtained by polymerizing β-D-glucose (β-D-glucopyranose) molecules represented by the following formula (1) via P (1→4) glycoside bond. Each of glucose units constituting cellulose has three hydroxy groups (where n represents a natural number). In the exemplary embodiment, using these hydroxy groups, the short-chain organic group and long-chain organic group can be introduced into the cellulose.

Cellulose is a main component of plants and can be obtained by a separation treatment for removing other components such as lignin from plants. Other than those thus obtained, cotton (for example, cotton linters) having a high cellulose content and pulp (for example, wood pulp) can be used directly or after they are purified. As the shape, size and form of the cellulose or a derivative thereof to be used as a raw material, a powder form cellulose or a derivative thereof having an appropriate particle size and particle shape is preferably used in view of reactivity, solid-liquid separation and handling. For example, a fibrous or powdery cellulose or a derivative thereof having a diameter of 1 to 100 μm (preferably 10 to 50 μm) and a length of 10 μm to 100 mm (preferably 100 μm to 10 mm) can be used.

The polymerization degree of cellulose in terms of degree of polymerization of glucose (average polymerization degree) preferably falls within the range of 50 to 5000, more preferably 100 to 3000 and further preferably 500 to 3000. If the polymerization degree is extremely low, the strength and heat resistance of the produced resin may not be sufficient in some cases. Conversely, if the polymerization degree is extremely high, the melt viscosity of the produced resin is extremely high, interfering with molding in some cases.

Cellulose may be mixed with chitin, chitosan, hemicellulose, xylan and glucomannan having an analogous structure. When cellulose is mixed with them, the amount thereof is preferably 30% by mass or less relative to the total amount of mixture, preferably 20% by mass or less and further preferably 10% by mass or less.

The description in the above is directed to cellulose; however, the present invention is applicable to analogs of the cellulose, such as general non-edible polysaccharides, i.e., chitin, chitosan, hemicellulose, xylan, glucomannan and curdlan.

(Long-Chain Component)

The cellulose resin according to an exemplary embodiment is formed by introducing a long-chain component as mentioned above in addition to a short-chain component as mentioned above by use of a hydroxy group of a cellulose.

Such a long-chain component can be introduced by reacting a hydroxy group of a cellulose with a long-chain reactant. The long-chain component corresponds to an acyl group introduced in place of a hydrogen atom of a hydroxy group of a cellulose. A long-chain organic group of the long-chain component and a pyranose ring of a cellulose can be bound via an ester bond. The acyl group introduced is a linear saturated aliphatic acyl group having 14 or more carbon atoms. A linear saturated aliphatic acyl group having 14 to 30 carbon atoms is mentioned; a linear saturated aliphatic acyl group having 14 to 22 carbon atoms is preferable; and groups (tetradecanoyl group, hexadecanoyl group, octadecanoyl group, icosanoyl group, docosanoyl group) obtained by removing OH from a carboxyl group of myristic acid, palmitic acid, stearic acid, arachidic acid and behenic acid, are more preferable.

The long-chain reactant is a compound having at least one functional group capable of reacting with a hydroxy group of a cellulose; for example, a compound having a carboxyl group, a carboxylic acid halide group or a carboxylic acid anhydride group can be used.

As the long-chain reactant, for example, a long-chain carboxylic acid having 14 or more carbon atoms and an acid halide or acid anhydride of the long-chain carboxylic acid can be used. The saturation degrees of these carboxylic acids or carboxylic acid derivatives are desirably as high as possible; a linear saturated fatty acid, an acid halide or anhydride thereof is preferable. Examples of the long-chain carboxylic acid include linear saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid and melissic acid. Myristic acid, palmitic acid, stearic acid, arachidic acid and behenic acid are preferable. Further as the long-chain carboxylic acid, a carboxylic acid obtained from natural products is preferable, in view of environmental harmony.

The long-chain component has preferably 14 or more carbon atoms and particularly preferably 16 or more carbon atoms. In view of reaction efficiency in introducing a long-chain component, the long-chain component has preferably 48 or less carbon atoms, more preferably 36 or less carbon atoms and particularly preferably 24 or less carbon atoms. A single type of a long-chain component may be contained alone, or two types or more of long-chain components may be contained.

The average number of long-chain components introduced per glucose unit of a cellulose (DS_(Lo)) (long-chain component introduction ratio), in other words, the average number of hydroxy groups substituted with a long-chain component (a linear saturated aliphatic acyl group having 14 or more carbon atoms) per glucose unit (hydroxy group substitution degree), preferably satisfy the conditions represented by the above expressions (1) and (2). DS_(Lo) can be set to fall within the range of, for example, 0.2 to 0.6, in accordance with the structure and introduction amount of a short-chain component, the structure of a long-chain component, physical properties required for a desired product and the production efficiency. In order to obtain a more sufficient introduction effect of a long-chain component, DS_(LO) is preferably 0.2 or more and more preferably 0.3 or more. In view of production efficiency and durability (e.g., strength, heat resistance), DS_(LO) is preferably 0.6 or less, more preferably 0.5 or less and further preferably 0.4 or less.

The properties of a cellulose or a derivative thereof can be improved by introducing a long-chain component as mentioned above into the cellulose or a derivative thereof. More specifically, water resistance, thermoplasticity and mechanical characteristics can be improved.

(Short-Chain Component)

The cellulose resin according to an exemplary embodiment is formed by introducing a short-chain component as mentioned above in addition to a long-chain component as mentioned above, using hydroxy groups of a cellulose. As the short-chain component, an acetyl group or a propionyl group, or both an acetyl group and a propionyl group, may be introduced.

Such a short-chain component can be introduced by reacting a hydroxy group of a cellulose with a short-chain reactant. The short-chain component corresponds to an acyl group moiety introduced in place of a hydrogen atom of a hydroxy group of a cellulose. The short-chain organic group (methyl group or propyl group) of a short-chain component and the pyranose ring of a cellulose can be bound via an ester bond.

The short-chain reactant is a compound having at least one functional group capable of reacting with a hydroxy group of a cellulose. Examples thereof include compounds having a carboxyl group, a carboxylic acid halide group and a carboxylic acid anhydride group. Specific examples thereof include an aliphatic monocarboxylic acid, an acid halide or acid anhydride thereof.

The short-chain component more preferably has 2 or 3 carbon atoms. It is preferable that a hydrogen atom of a hydroxyl group of a cellulose is replaced with an acyl group (acetyl group or propionyl group) having 2 or 3 carbon atoms.

The average number of short-chain components introduced per glucose unit of a cellulose (DS_(SH)) (short-chain component introduction ratio), in other words, the average number of hydroxy groups substituted with a short-chain component (acetyl group or/and propionyl group) per glucose unit (the substitution degree of hydroxy groups), preferably satisfy the conditions represented by the above expressions (1) and (2) (note that, 3≥DS_(Lo)+DS_(Sh)). DS_(SH) can be set to fall within the range of 1.7 to 2.8. In order to obtain a more sufficient effect of introducing a short-chain component, DS_(SH) is preferably 1.7 or more. Particularly, in view of, e.g., water resistance and flowability, DS_(SH) is preferably 1.9 or more, more preferably 2.0 or more and further preferably 2.2 or more. In order to obtain the sufficient effect of a long-chain component in addition to the effect of introducing a short-chain component, DS_(SH) is preferably 2.8 or less, more preferably 2.7 or less and further preferably 2.6 or less.

By introducing the aforementioned short-chain component into a cellulose or a derivative thereof, the intermolecular force (intermolecular bond) of the cellulose can be reduced; and mechanical characteristics such as elastic modulus, chemical resistance and physical properties such as surface hardness can be enhanced.

The ratio of a long-chain component and a short-chain component (DS_(Sh)/DS_(Lo)) is preferably 4 or more and 12 or less. If the ratio is less than 4, the material becomes excessively flexible, with the result that strength/heat resistance tend to decrease. In contrast, if the ratio exceeds 12, thermoplasticity becomes insufficient, with the result that the material becomes unsuitable for molding.

(Residual Amount of Hydroxy Group in Cellulose Resin)

As the residual amount of hydroxy groups increases, the maximum strength and heat resistance of the cellulose resin tend to increase; whereas water absorbability tends to increase. In contrast, as the conversion rate (degree of substitution) of hydroxy groups increases, water absorbability tends to decrease, plasticity and breaking strain tend to increase; whereas, maximum strength and heat resistance tend to decrease. In consideration of these tendencies etc., the conversion rate of hydroxy groups can be appropriately set.

The average number of the remaining hydroxy group per glucose unit (hydroxy group remaining degree, DS_(OH)) of a final cellulose resin can be set to fall within the range of 0 to 0.9 (note that, DS_(Lo)+DS_(Sh)+DS_(OH)=3). In view of mechanical characteristics such as maximum strength and durability such as heat resistance, a hydroxy group may remain. For example, the hydroxy group remaining degree can be set at 0.01 or more and further 0.1 or more. Particularly, in view of flowability, the hydroxy group remaining degree of a final cellulose resin is preferably 0.1 or more and more preferably 0.2 or more. In view of, e.g., water resistance in addition to flowability, the hydroxy group remaining degree is preferably 0.9 or less. Further in view of, e.g., impact resistance, the hydroxy group remaining degree is preferably 0.6 or less and more preferably 0.5 or less.

(Activation of Cellulose)

Before the reaction step for introducing a long-chain component and a short-chain component into a cellulose, an activation treatment (pretreatment step) can be performed in order to increase the reactivity of the cellulose. As the activation treatment, an activation treatment which is routinely performed before acetylation of a cellulose can be applied.

In the activation treatment, a cellulose is swollen by bringing the cellulose into contact with a solvent, for example, by a method of spraying an activation solvent having affinity for a cellulose to the cellulose or by a method (soaking method) of soaking a cellulose in an activation solvent. Owing to the treatment, a reactant easily penetrates between cellulose molecular chains (if a solvent and a catalyst are used, a reactant easily penetrates together with these), with the result that the reactivity of the cellulose improves. Herein, examples of the activation solvent include water; carboxylic acids such as acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid and stearic acid; alcohols such as methanol, ethanol, propanol and isopropanol; nitrogen-containing compounds such as dimethylformamide, formamide, ethanolamine and pyridine; and sulfoxide compounds such as dimethylsulfoxide. These can be used in combination of two or more types. Particularly preferably, water, acetic acid, pyridine and dimethylsulfoxide can be used.

A cellulose can be activated by putting it in a long-chain fatty acid. If the melting point of the long-chain fatty acid is room temperature or more, a cellulose can be heated up to the melting point or more.

The use amount of activation solvent relative to a cellulose (100 parts by mass) can be set to be, for example, 10 parts by mass or more, preferably 20 parts by mass or more and more preferably 30 parts by mass or more. If a cellulose is soaked in an activation solvent, the use amount of activation solvent relative to the cellulose in term of mass, can be set to be, for example, the same or more, preferably 5 times or more and more preferably 10 times or more. In view of load for removing an activation solvent after the pretreatment and cost reduction of materials, the use amount of activation solvent is preferably 300 times or less, more preferably 100 times or less and further preferably 50 times or less.

The temperature of the activation treatment can be appropriately set within the range of, for example, 0 to 100° C. In view of the efficiency of activation and reduction of energy cost, the temperature is preferably 10 to 40° C. and more preferably 15 to 35° C.

When a cellulose is put in a melted long-chain fatty acid, the cellulose can be heated up to melting point or more of the long-chain fatty acid.

The time for the activation treatment can be appropriately set within the range of, for example, 0.1 hour to 72 hours. In order to perform sufficient activation and reduce the treatment time, the time is preferably 0.1 hour to 24 hours and more preferably 0.5 hours to 3 hours.

After the activation treatment, an excessive activation solvent can be removed by a solid-liquid separation method such as suction filtration, filter press and compression.

The activation solvent contained in a cellulose can be substituted with the solvent to be used in the reaction after the activation treatment. For example, a substitution treatment can be performed in accordance with the soaking method for an activation treatment mentioned above by changing the activation solvent to the solvent to be used in the reaction.

(Method for Introducing Long-Chain Component and Short-Chain Component)

A cellulose derivative (cellulose resin) according to an exemplary embodiment can be produced in accordance with the method shown below.

A process for producing a cellulose derivative according to an exemplary embodiment includes a step of acylating hydroxy groups of a cellulose constituting pulp by reacting, in an organic solvent, the pulp dispersed in the organic solvent, a short-chain reactant (short-chain acylating agent) and a long-chain reactant (long-chain acylating agent) in the presence of an acid trapping component while warming. It is preferable that the short-chain reactant (short-chain acylating agent) and the long-chain reactant (long-chain acylating agent) are dissolved in the solvent. The acid trapping component may be also used as a solvent.

As a long-chain reactant for introducing a long-chain component in a cellulose, an acid chloride of a linear saturated fatty acid as mentioned above is preferable. A single type of a long-chain reactant may be used alone or two types or more of long-chain reactants may be used in combination. As a short-chain reactant for introducing a short-chain component in a cellulose, a compound selected from acetyl chloride, acetic anhydride, propionic anhydride and propionyl chloride is preferable. A single type of a short-chain reactant may be used alone or two types or more of short-chain reactants may be used in combination.

The addition amounts of the long-chain reactant and short-chain reactant can be set in accordance with the degree of substitution (DS_(Lo)) with a long-chain component and the degree of substitution (DS_(Sh)) with a short-chain component in a desired cellulose derivative. If the short-chain reactant is excessively present, the binding amount of a long-chain component decreases and the degree of substitution (DS_(Lo)) with a long-chain component tends to decrease.

As the organic solvent, a solvent providing a liquid holding rate by cellulose: 90 vol % or more, is preferably used.

The “liquid holding rate” can be measured as follows.

Filter paper (5B, 40 mmϕ, water content: about 2%) made of cotton fiber is soaked in each solvent at room temperature for one hour. The weights of the filter paper before and after soaking are measured and assigned to the following expression. In this manner, a liquid holding rate (vol %) is obtained. The weight of a sample after soaking is measured at the time when dripping of a solvent from the sample is stopped. Liquid holding rate (vol %)=(weight after soaking−weight before soaking)/weight before soaking/specific gravity of solvent×100

Examples of a solvent providing a liquid holding rate of 90 vol % or more, include water (liquid holding rate: 145 vol %), acetic acid (liquid holding rate: 109 vol %), dioxane (liquid holding rate: 93 vol %), pyridine (liquid holding rate: 109 vol %), N-methyl pyrrolidone (liquid holding rate: 104 vol %), N,N-dimethylacetamide (liquid holding rate: 112 vol %), N,N-dimethylformamide (liquid holding rate: 129 vol %) and dimethylsulfoxide (liquid holding rate: 180 vol %).

An acid trapping component is not particularly limited as long as it is a base neutralizing an acid (e.g., hydrochloric acid, acetic acid, propionic acid) produced as a by-product. Examples thereof include alkaline metal hydroxides such as sodium hydroxide and potassium hydroxide; alkaline earth metal hydroxides such as calcium hydroxide and barium hydroxide; metal alkoxides such as sodium methoxide, sodium ethoxide; and nitrogen-containing nucleophilic compounds such as diazabicycloundecene, diazabicyclononene, triethylamine and pyridine. Of them, triethylamine and pyridine are preferable since they can be used also as a solvent and pyridine is particularly preferable. When an acid trapping component is added independently of a solvent, it is preferable that the acid trapping component is present in a reaction system from the initiation time of a reaction. As long as an acid trapping component is present in a reaction system from the initiation time of a reaction, an acid trapping component may be added before or after addition of an acylating agent.

The addition amount of an acid trapping component relative to the total amount of a starting long-chain reactant (long-chain acylating agent) and a starting short-chain reactant (short-chain acylating agent) is preferably 0.1 to 10 equivalents and more preferably 0.5 to 5 equivalents. However, when a nitrogen-containing nucleophilic compound is used as a solvent, the addition amount of an acid trapping component is not limited the above range. If the addition amount of an acid trapping component is small, an acylation reaction efficiency decreases. In contrast, if the addition amount of an acid trapping component is large, the cellulose may be decomposed and sometimes reduced in molecular weight.

The reaction temperature in the acylation step is preferably 50 to 100° C. and more preferably 75 to 95° C. The reaction time can be set at 2 hours to 5 hours and preferably 3 hours to 4 hours. If the reaction temperature is sufficiently high, the reaction speed can be increased, with the result that an acylation reaction can be completed in a relative short time and the reaction efficiency can be increased. If the reaction temperature falls within the above range, a decrease in molecular weight by heating can be suppressed.

The amount of an organic solvent can be set to be 10 to 50 times and preferably 20 to 40 times (mass ratio) as large as the amount (dry mass) of the raw material pulp.

(Aging Step)

After the above acylation step, an aqueous alkaline solution is added, and the reaction solution is preferably held (aged) as it is while warming. The temperature during the aging is preferably 25 to 75° C. and preferably 40 to 70° C. The time for aging can be set to fall within the range of 1 to 5 hours and preferably 1 to 3 hours.

The addition amount of an aqueous alkaline solution can be set so as to correspond to 3 to 30% by mass relative to the solvent to be used, and preferably 5 to 20% by mass.

As the aqueous alkaline solution, aqueous solutions of, e.g., potassium hydroxide, sodium carbonate and sodium hydrogen carbonate are mentioned, and an aqueous solution of sodium hydroxide is preferable. The concentration of an aqueous alkaline solution is preferably 1 to 30% by mass and more preferably 5 to 20% by mass.

Owing to such an aging step, the long-chain component and the short-chain component once bound are partially hydrolyzed to come back to (homogeneous) hydroxy groups, with the result that mechanical characteristics such as strength and impact resistance can be enhanced. In addition, in the following precipitation step, a product having satisfactory properties (fine granules) can be obtained.

(Recovery Step)

A cellulose derivative (product), which is formed by introducing a long-chain component and a short-chain component, can be recovered from a reaction solution in accordance with a recovery method generally used. The recovery method is not limited; however, if a product is not dissolved in a reaction solution, a solid-liquid separation method for separating a reaction solution and a product is preferable in view of production energy. If it is difficult to separate a solid and a liquid because a product is dissolved in or compatible with a reaction solution, the reaction solution is distilled off and a product can be recovered as the residue. Alternatively, a poor solvent for a product is added to the reaction solution to precipitate the product, which may be recovered by solid-liquid separation.

When a reaction solution is distillated, it is preferable to use a short-chain reactant, a reaction solvent and a catalyst having low boiling points. The catalyst can be removed from a product with, e.g., a washing solvent without distillation. When components except a product, such as a solvent, are distilled away from a reaction solution, distillation is stopped when a product is precipitated, and then, the remaining reaction solution and the precipitated product can be subjected to solid-liquid separation to recovery the product.

As the solid-liquid separation method, e.g., filtration (natural filtration, filtration under reduced pressure, pressure filtration, centrifugal filtration and these while applying heat), spontaneous sedimentation and flotation, separation (by funnel), centrifugal separation and squeeze, are mentioned. These can be used appropriately in combination.

A product (a cellulose derivative) dissolved in a filtrate after the solid-liquid separation can be precipitated by adding a poor solvent for the product and further subjected to solid-liquid separation to recover it.

The solid content (a cellulose derivative) recovered from a reaction solution is, if necessary washed and dried by a method generally employed.

The cellulose derivative produced by this method can possess a reinforcing crystal structure due to a cellulose main-chain crystal in a thermoplastic matrix. This is derived from an unreacted part when a cellulose material is acylated. Such a cellulose main-chain crystal can be evaluated, for example, by X-ray diffractometry. At the time of evaluation, for example, a cellulose derivative can be pressed to increase the density, thereby facilitating detection of a signal.

(Other Process for Producing Cellulose Derivative)

A cellulose resin can be obtained by acylating a cellulose in a solid-liquid heterogeneous system using a mixed acid anhydride containing a long-chain component and a short-chain component, as an acylating agent. Cellulose is preferably activated. The activation treatment can be performed by a method generally used.

Acylation can be carried out in a solvent which provides a liquid holding rate of 90% or more (for example, dioxane, in an amount of, e.g., 80 to 120 times as large as the dry weight of pulp), in the presence of an acid catalyst (for example, sulfuric acid) while stirring at 45 to 65° C. for 2 to 5 hours. Thereafter, it is preferable that water is added to age the reaction solution for a few hours (for example, 1 to 3 hours) while heating (for example, 55 to 75° C.).

After completion of the reaction, a poor solvent such as a water/methanol solvent mixture, is added to allow a product dissolved in the liquid phase to sufficiently precipitate, and then, solid-liquid separation can be performed to recover a product. Thereafter, washing and drying can be made.

Acylation can be performed in a homogeneous solution system in which a cellulose and an acylating agent are homogenously dissolved in a solvent. A cellulose is preferably activated. The activation treatment can be performed by a method generally used.

As a solvent for acylation, a solvent such as N,N-dimethylacetamide, which can dissolve a cellulose, is used.

As the acylating agent, a mixed acid anhydride having a long-chain component and a short-chain component, which is produced in the same solvent as the solvent to be used in acylation, can be used.

After completion of the reaction, a poor solvent such as methanol is added to precipitate a product, which may be recovered by solid-liquid separation. Thereafter, washing and drying can be made.

(Molding Resin Composition and Additives)

The cellulose derivative according to an exemplary embodiment can provide a resin composition suitable as a molding material by adding additives in accordance with desired properties. The cellulose derivative can be compatible with an additive which is compatible with a general cellulose derivative.

To the cellulose derivative according to an exemplary embodiment, various types of additives usually used in thermoplastic resins can be applied. For example, if a plasticizer is added, thermoplasticity and breaking elongation while breaking can be more improved. Examples of such a plasticizer include phthalic esters such as dibutyl phthalate, diaryl phthalate, diethyl phthalate, dimethyl phthalate, di-2-methoxyethyl phthalate, ethyl phthalyl ethyl glycolate and methyl phthalyl ethyl glycolate; tartaric acid esters such as dibutyl tartrate; adipic acid esters such as dioctyl adipate and diisononyl adipate; polyhydric alcohol esters such as triacetin, diacetyl glycerin, tripropionitrile glycerin and glyceryl monostearate; phosphoric acid esters such as triethyl phosphate, triphenyl phosphate and tricresyl phosphate; dibasic fatty acid esters such as dibutyl adipate, dioctyl adipate, dibutyl azelate, dioctyl azelate and dioctyl sebacate; citric acid esters such as triethyl citrate, acetyltriethyl citrate and tributyl acetylcitrate; epoxylated vegetable oils such as epoxylated soybean oil and epoxylated linseed oil; castor oil and a derivative thereof; benzoic acid esters such as ethyl O-benzoyl benzoate; aliphatic dicarboxylic acid esters such as sebacate and azelate; unsaturated dicarboxylic acid esters such as maleate; and N-ethyl toluene sulfonamide, triacetin, O-cresyl p-toluenesulfonate and tripropionin. Particularly of them, if a plasticizer such as dioctyl adipate, benzyl adipate-2 butoxyethoxyethyl, tricresyl phosphate, diphenylcresyl phosphate or diphenyl octyl phosphate is added, not only thermoplasticity and breaking elongation but also shock resistance can be effectively improved.

Examples of other plasticizers include cyclohexane dicarboxylic acid esters such as dihexyl cyclohexanedicarboxylate, dioctyl cyclohexanedicarboxylate and di-2-methyloctyl cyclohexanedicarboxylate; trimellitic acid esters such as dihexyl trimellitate, diethylhexyl trimellitate and dioctyl trimellitate; and pyromellitic acid esters such as dihexyl pyromellitate, diethylhexyl pyromellitate and dioctyl pyromellitate.

To the cellulose derivative according to an exemplary embodiment, if necessary, an inorganic or organic granular or fibrous filler can be added. By adding a filler, strength and rigidity can be more improved. Examples of the filler include, mineral particles (talc, mica, baked siliceous earth, kaolin, sericite, bentonite, smectite, clay, silica, quartz powder, glass beads, glass powder, glass flake, milled fiber, Wollastonite, etc.), boron-containing compounds (boron nitride, boron carbonate, titanium boride etc.), metal carbonates (magnesium carbonate, heavy calcium carbonate, light calcium carbonate, etc.), metal silicates (calcium silicate, aluminum silicate, magnesium silicate, magnesium aluminosilicate, etc.), metal oxides (magnesium oxide etc.), metal hydroxides (aluminum hydroxide, calcium hydroxide, magnesium hydroxide, etc.), metal sulfates (calcium sulfate, barium sulfate, etc.), metal carbides (silicon carbide, aluminum carbide, titanium carbide, etc.), metal nitrides (aluminum nitride, silicon nitride, titanium nitride, etc.), white carbon and metal foils. Examples of the fibrous filler include organic fibers (natural fiber, papers etc.), inorganic fibers (glass fiber, asbestos fiber, carbon fiber, silica fiber, silica alumina fiber, Wollastonite, zirconia fiber, potassium titanate fiber etc.) and metal fibers. These fillers can be used singly or in combination of two or more types.

To the cellulose derivative according to an exemplary embodiment, if necessary, a flame retardant can be added. By adding a flame retardant, flame resistance can be imparted. Examples of the flame retardant include metal hydrates such as magnesium hydroxide, aluminum hydroxide and hydrotalcite, basic magnesium carbonate, calcium carbonate, silica, alumina, talc, clay, zeolite, bromine-based flame retardant, antimony trioxide, phosphoric acid based flame retardant (aromatic phosphate, aromatic condensed phosphate, etc.), compounds containing phosphorus and nitrogen (phosphazene compound), etc. These flame retardants can be used singly or in combination with two or more types.

To the cellulose derivative according to an exemplary embodiment, if necessary, a shock resistance improver can be added. By adding a shock resistance improver, shock resistance can be improved. Examples of the shock resistance improver include a rubber component and a silicone compound. Examples of the rubber component include a natural rubber, epoxylated natural rubber and synthesized rubber. Furthermore, examples of the silicone compound include organic polysiloxane formed by polymerization of alkyl siloxane, alkyl phenyl siloxane, etc. and modified silicone compounds obtained by modifying a side chain or an end of an organic polysiloxane as mentioned above with polyether, methylstyryl, alkyl, higher fatty acid ester, alkoxy, fluorine, an amino group, an epoxy group, a carboxyl group, a carbinol group, a methacryl group, a mercapto group, a phenol group etc. These shock resistance improvers can be used singly or in combination of two or more types.

As the silicone compound, a modified silicone compound (modified polysiloxane compound) is preferred. As the modified silicone compound, a modified polydimethyl siloxane is preferred, which has a structure having a main chain constituted of dimethyl siloxane repeat units and a side chain or a terminal methyl group partly substituted with an organic substituent containing at least one group selected from an amino group, an epoxy group, a carbinol group, a phenol group, a mercapto group, a carboxyl group, a methacryl group, a long-chain alkyl group, an aralkyl group, a phenyl group, a phenoxy group, an alkyl phenoxy group, a long-chain fatty acid ester group, a long-chain fatty acid amide group and a polyether group. The modified silicone compound, because of the presence of such an organic substituent, is improved in affinity for the aforementioned cellulose derivative and dispersibility in the cellulose derivative is improved. Consequently, a resin composition excellent in shock resistance can be obtained.

As such a modified silicone compound, a modified silicone compound produced in accordance with a conventional method can be used.

Examples of the organic substituent contained in the modified silicone compound include the organic substituents represented by the following formulas (2) to (20) are mentioned:

where a and b each represent an integer of 1 to 50.

In the aforementioned formulas, R¹ to R¹⁰, R¹² to R¹⁵, R¹⁹ and R²¹ each represent a divalent organic group. Examples of the divalent organic group include alkylene groups such as a methylene group, an ethylene group, a propylene group and a butylene group; alkyl arylene groups such as a phenylene group and a tolylene group; oxyalkylene groups and polyoxyalkylene groups such as —(CH₂—CH₂—O)c- (c represents an integer from 1 to 50), —[CH₂—CH(CH₃)—O]_(d)— (d represents an integer from 1 to 50), and —(CH₂)e-NHCO— (e represents an integer from 1 to 8). Of these, an alkylene group is preferable and particularly, an ethylene group and a propylene group are preferable.

In the aforementioned formulas, R¹¹, R¹⁶ to R¹⁸, R²⁰ and R²² each represent an alkyl group having at most 20 carbon atoms. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group and a pentadecyl group. Furthermore, the structures of the above alkyl groups may have one or more unsaturated bonds.

The total average content of organic substituents in a modified silicone compound desirably falls within the range where the modified silicone compound having an appropriate particle diameter (for example, 0.1 μm or more and 100 μm or less) can be dispersed in a matrix, i.e., a cellulose derivative, during a process for producing a cellulose derivative composition. If a modified silicone compound having an appropriate particle diameter is dispersed in a cellulose derivative, stress concentration on the periphery of a silicone region having a low elastic modulus effectively occurs. As a result, a resin molded body having excellent shock resistance can be obtained. The total average content of such organic substituents is preferably 0.01% by mass or more and more preferably 0.1% by mass or more, and also preferably 70% by mass or less and more preferably 50% by mass or less. If an organic substituent is contained appropriately, the modified silicone compound can be improved in affinity for a cellulose resin, the modified silicone compound having an appropriate particle diameter can be dispersed in a cellulose derivative, and further bleed out due to separation of the modified silicone compound in a molding can be suppressed. If the total average content of the organic substituents is excessively low, it becomes difficult to disperse a modified silicone compound having an appropriate particle diameter in a cardanol-added cellulose resin.

If an organic substituent of the modified polydimethyl siloxane compound is an amino group, an epoxy group, a carbinol group, a phenol group, a mercapto group, a carboxyl group or a methacryl group, the average content of the organic substituent in the modified polydimethyl siloxane compound can be obtained by the following Expression (I). Organic substituent average content (%)=(organic substituent formula-weight/organic substituent equivalent)×100  (I)

In the Expression (I), the organic substituent equivalent is an average mass of a modified silicone compound per organic substituent (1 mole).

When the organic substituent of the modified polydimethyl siloxane compound is a phenoxy group, an alkylphenoxy group, a long-chain alkyl group, an aralkyl group, a long-chain fatty acid ester group or a long-chain fatty acid amide group, the average content of the organic substituent of the modified polydimethyl siloxane compound can be obtained from the following Expression (II). Organic substituent average content (%)=x×w/[(1−x)×74+x×(59+w)]×100  (II)

In the Expression (II), x is an average molar fraction of the organic substituent-containing a siloxane repeat unit relative to all siloxane repeat units of the modified polydimethyl siloxane compound; and w is the formula weight of the organic substituent.

In the case where the organic substituent of the modified polydimethyl siloxane compound is a phenyl group, the average content of the phenyl group in the modified polydimethyl siloxane compound can be obtained by the following Expression (III). Phenyl group average content (%)=154×x/[74×(1−x)+198×x]×100  (III)

In the Expression (III), x is an average molar fraction of the phenyl group-containing siloxane repeat unit relative to all siloxane repeat units in the modified polydimethyl siloxane compound (A).

In the case where the organic substituent of the modified polydimethyl siloxane compound is a polyether group, the average content of the polyether group in the modified polydimethyl siloxane compound can be obtained by the following Expression (IV). Polyether group average content (%)=HLB value/20×100  (IV)

In the Expression (IV), the HLB value represents the degree of affinity of a surfactant for water and oil, and is defined by the following Expression (V) based on the Griffin Act. HLB value=20×(sum of formula weights of hydrophilic moieties/molecular weight)  (V)

To the cellulose derivative of the exemplary embodiment, two or more modified silicone compounds having different affinities to the derivative may be added. In this case, dispersibility of a relative low-affinity modified silicone compound (A1) is improved by a relative high-affinity modified silicone compound (A2) to obtain a cellulose resin composition having even more excellent shock resistance. The total average content of an organic substituent of the relatively low-affinity modified silicone compound (A1) is preferably 0.01% by mass or more and more preferably 0.1% by mass or more and also preferably 15% by mass or less and more preferably 10% by mass or less. The total average content of an organic substituent of the relatively high-affinity modified silicone compound (A2) is preferably 15% by mass or more and more preferably 20% by mass or more and also preferably 90% by mass or less.

The blending ratio (mass ratio) of the modified silicone compound (A1) to the modified silicone compound (A2) can be set to fall within the range of 10/90 to 90/10.

In a modified silicone compound, dimethyl siloxane repeat units and organic substituent-containing siloxane repeat units each of which may be homologously and continuously connected, alternately connected or connected at random. A modified silicone compound may have a branched structure.

The number average molecular weight of a modified silicone compound is preferably 900 or more and more preferably 1000 or more, and also preferably 1000000 or less, more preferably 300000 or less and further preferably 100000 or less. If the molecular weight of a modified silicone compound is sufficiently large, loss by vaporization can be suppressed in kneading with a melted cellulose derivative during a process for producing a cellulose derivative composition. Furthermore, if the molecular weight of a modified silicone compound is appropriate (not excessively large), a uniform molding having good dispersibility can be obtained.

As the number average molecular weight, a value (calibrated by a polystyrene standard sample) obtained by measuring a 0.1% chloroform solution of a sample by GPC can be employed.

The addition amount of such a modified silicone compound is preferably, in view of obtaining sufficient addition effect, 1% by mass or more relative to the total cellulose derivative composition and more preferably 2% by mass or more. In view of sufficiently ensuring properties of a cellulose resin such as strength and suppressing bleed out, the addition amount of a modified silicone compound is preferably 20% by mass or less and more preferably 10% by mass or less.

By adding such a modified silicone compound to a cellulose derivative, the modified silicone compound having an appropriate particle diameter (for example, 0.1 to 100 μm) can be dispersed in the resin and the shock resistance of a resin composition can be improved.

To the cellulose derivative of the exemplary embodiment, if necessary, additives such as a colorant, an antioxidant and a heat stabilizer may be added as long as they are applied to conventional resin compositions.

To the cellulose derivative of the exemplary embodiment, if necessary, a general thermoplastic resin may be added.

As the thermoplastic resin, a polyester can be added and a straight-chain aliphatic polyester can be preferably used. As the straight-chain aliphatic polyester (Y), the following straight-chain aliphatic polyesters (Y1) and (Y2) are preferable, for example, polybutylene succinate, polybutylene succinate adipate and polycaprolactone can be mentioned.

(Y1) Straight-chain aliphatic polyester containing at least one of repeating units represented by the following formula (VI) and formula (VII) —(CO—R²³—COO—R²⁴—O—)—  (VI) —(CO—R²⁵—O—)—  (VII)

In the formula (VI), R²³ represents a divalent aliphatic group having carbon atoms of 1 to 12, preferably 2 to 8 and more preferably 2 to 4; and R²⁴ represents a divalent aliphatic group having carbon atoms of 2 to 12, preferably 2 to 8 and more preferably 2 to 4.

In the formula (VII), R²⁵ represents a divalent aliphatic group having carbon atoms of 2 to 10, preferably 2 to 8 and more preferably 2 to 4.

(Y2) Straight-chain aliphatic polyester composed of a product obtained by ring-opening polymerization of a cyclic ester.

The straight-chain aliphatic polyester (Y1) can be obtained by a condensation reaction between at least one selected from the group consisting of, for example, an aliphatic dicarboxylic acid, an acid anhydride thereof and a diester thereof, and an aliphatic diol.

The aliphatic dicarboxylic acid has carbon atoms of, for example, 3 to 12, preferably 3 to 9, more preferably 3 to 5. The aliphatic carboxylic acid is, for example, an alkane dicarboxylic acid. Specific examples thereof include malonic acid, succinic acid, adipic acid, sebacic acid, azelaic acid and dodecane dicarboxylic acid. The aliphatic dicarboxylic acids, for example, may be used alone or in combination of two or more.

The aliphatic diol has carbon atoms of, for example, 2 to 12, preferably 2 to 8 and more preferably 2 to 6. The aliphatic diol is, for example, an alkylene glycol. Specific examples thereof include ethylene glycol, 1,3-propylene glycol, 1,4-butane diol, 1,6-hexane diol, 1,9-nonane diol, 1,10-decane diol and 1,12-dodecane diol. Of them, a straight-chain aliphatic diol having 2 to 6 carbon atoms is preferable, and particularly, ethylene glycol, 1,3-propylene glycol, 1,4-butane diol and 1,6-hexane diol are preferable. The aliphatic diols, for example, may be used alone or in combination of two or more.

The straight-chain aliphatic polyester (Y2) is a straight-chain aliphatic polyester obtained by ring-opening polymerization of a cyclic ester. The cyclic ester is, for example, lactone having carbon atoms of 2 to 12. Specific examples thereof include, α-acetolactone, β-propiolactone, γ-butyrolactone and δ-valerolactone. The cyclic esters, for example, may be used alone or in combination with two or more.

The number average molecular weight of the straight-chain aliphatic polyester (Y) is not particularly limited. The lower limit thereof is preferably, for example, 10000 or more, and more preferably 20000 or more. The upper limit thereof is preferably, for example, 200000 or less and more preferably 100000 or less. The aliphatic polyester having a molecular weight within the above range can provide, for example, a more uniform molded body having more excellent dispersibility.

As the number average molecular weight, for example, a value (calibrated by a polystyrene standard sample) obtained by measuring a 0.1% chloroform solution of a sample by GPC can be employed.

By adding a thermoplastic resin having excellent flexibility such as a thermoplastic polyurethane elastomer (TPU) to the cellulose derivative according to an exemplary embodiment, shock resistance can be improved. The addition amount of such a thermoplastic resin (particularly, TPU) is, in view of obtaining sufficient addition effect, preferably 1% by mass or more and more preferably 5% by mass or more relative to the total composition containing the cellulose resin of the exemplary embodiment.

The thermoplastic polyurethane elastomer (TPU) suitable for improving shock resistance that can be used includes a polyurethane elastomer prepared by using a polyol, a diisocyanate and a chain extender.

Examples of the polyol include polyester polyol, polyester ether polyol, polycarbonate polyol and polyether polyol.

Examples of the polyester polyol include a polyester polyol obtained by a dehydration condensation reaction between a polyvalent carboxylic acid such as an aliphatic dicarboxylic acid (succinic acid, adipic acid, sebacic acid, azelaic acid, etc.), an aromatic dicarboxylic acid (phthalic acid, terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, etc.), an alicyclic dicarboxylic acid (hexahydrophthalic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, etc.), or an acid ester or an acid anhydride of each of these, and a polyol such as ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,3-butane diol, 1,4-butane diol, 1,5-pentane diol, 1,6-hexane diol, 3-methyl-1,5-pentane diol, neopentyl glycol, 1,3-octane diol, 1,9-nonane diol, or a mixture of these; and a polylactone diol obtained by ring-opening polymerization of a lactone monomer such as ε-caprolactone.

Examples of the polyester ether polyol include a compound obtained by a dehydration condensation reaction between a polyvalent carboxylic acid such as an aliphatic dicarboxylic acid (succinic acid, adipic acid, sebacic acid, azelaic acid, etc.), an aromatic dicarboxylic acid (phthalic acid, terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, etc.), an alicyclic dicarboxylic acid (hexahydrophthalic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, etc.), or an acid ester or an acid anhydride of each of these, and a glycol such as diethylene glycol or an alkylene oxide adduct (propylene oxide adduct etc.) or a mixture of these.

Examples of the polycarbonate polyol include a polycarbonate polyol obtained by reacting one or two or more polyols such as ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,3-butane diol, 1,4-butane diol, 1,5-pentane diol, 1,6-hexane diol, 3-methyl-1,5-pentane diol, neopentyl glycol, 1,8-octane diol, 1,9-nonane diol and diethylene glycol with diethylene carbonate, dimethyl carbonate, diethyl carbonate, etc.; and further may include a copolymer of a polycaprolactone polyol (PCL) and a polyhexamethylene carbonate (PHL).

Examples of the polyether polyol include a polyethylene glycol, polypropylene glycol and polytetramethylene ether glycol, each of which is obtained by polymerizing respective cyclic ethers: ethylene oxide, propylene oxide and tetrahydrofuran; and copolyethers of these.

Examples of the diisocyanate to be used in formation of TPU include tolylene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), tolidine diisocyanate, 1,6-hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), xylylene diisocyanate (XDI), hydrogenated XDI, triisocyanate, tetramethyl xylene diisocyanate (TMXDI), 1,6,11-undecane triisocyanate, 1,8-diisocyanatemethyl octane, lysine ester triisocyanate, 1,3,6-hexamethylene triisocyanate, bicycloheptane triisocyanate and dicyclohexyl methane diisocyanate (hydrogenated MDI; HMDI). Of these, 4,4′-diphenylmethane diisocyanate (MDI) and 1,6-hexamethylene diisocyanate (HDI) are preferably used.

Examples of the chain extender to be used in formation of TPU, a low-molecular weight polyol can be used. Examples of the low-molecular weight polyol include aliphatic polyols such as ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,3-butane diol, 1,4-butane diol, 1,5-pentane diol, 1,6-hexane diol, 3-methyl-1,5-pentane diol, neopentyl glycol, 1,8-octane diol, 1,9-nonane diol, diethylene glycol and 1,4-cyclohexane dimethanol and glycerin; and aromatic glycols such as 1,4-dimethylolbenzene, bisphenol A and ethylene oxide or a propylene oxide adduct of bisphenol A.

When a silicone compound is copolymerized with a thermoplastic polyurethane elastomer (TPU) obtained from these materials, further excellent shock resistance can be obtained.

These thermoplastic polyurethane elastomers (TPU) may be used singly or in combination.

A process for producing a resin composition containing the cellulose derivative according to an exemplary embodiment, additives and a thermoplastic resin, is not particularly limited. For example, the resin composition can be produced by melting and mixing additives and the cellulose resin manually by handmixing or by use of a known mixer such as a tumbler mixer, or a ribbon blender, a single-axial or a multiaxial mixing extruder, and a compounding apparatus such as a kneader and kneading roll and, if necessary, granulating the mixture into an appropriate shape. In another preferable process, additives dispersed in solvent such as an organic solvent and a resin are mixed and furthermore, if necessary, a coagulation solvent is added to obtain a mixed composition of the additives and the resin and thereafter, the solvent is evaporated.

The cellulose resin according to the exemplary embodiments mentioned above can be used as a base resin for a molding material (resin composition). The molding material using the cellulose resin as a base resin is suitable for forming a molded body such as housing, e.g. packaging for an electronic device.

The base resin herein refers to a main component of the molding material and means that other components may be contained as long as the components do not prevent the function of the main component. The content rate of the main component is not particularly limited; however, the content rate of the main component in a composition is 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more and particularly preferably 90% by mass or more.

EXAMPLES

The present invention will be more specifically described by way of examples below.

(Example A1) (Cellulose Propionate Stearate)

After a treatment for activating a cellulose was performed, the cellulose was acylated in a solid-liquid heterogeneous system to obtain a cellulose resin. More specifically, the cellulose resin was prepared as follows.

Six grams (in terms of dry weight, 37 mmol/glucose unit) of cellulose (derived from a broad-leaf tree, pre-hydrolyzed craft pulp, water content: 8.3%) was cut into pieces having a several cm in size, put in a reactor and dispersed in pyridine (240 ml) in a nitrogen atmosphere and stirred at room temperature overnight. In this manner, the cellulose was activated.

Thereafter, the solution was cooled up to about 10° C. Stearoyl chloride (5.60 g (19 mmol)) and propionyl chloride (10.96 g (118 mmol)) were previously mixed and put in the reactor.

The reaction solution was stirred at 90° C. for 4 hours, and then, a 13% aqueous sodium hydroxide solution (23 g) was slowly added dropwise. The reaction solution was stirred for one hour while cooling it to 40° C.

Water (260 ml) was further added to precipitate a product. The product was recovered by suction filtration. The solid content obtained was washed twice with 200 ml of water and then washed (3 to 4 times) with 200 ml of methanol until the color of the filtrate disappeared.

The solid content washed was dried in vacuum at 105° C. for 5 hours to obtain 13.0 g (yield 98%) of a powdery cellulose resin (cellulose propionate stearate).

The resultant sample (cellulose propionate stearate) was measured by ¹H-NMR (AV-400, manufactured by Bruker, 400 MHz, solvent: CDCl₃ (partial dissolution)). As a result, DS_(Lo) was 0.24 and DS_(Sh) was 2.31.

This sample was evaluated in accordance with the following criteria. The results are shown in Table 1.

[Pelletization of Powdery Sample by Kneading]

A sample (7.5 g) was kneaded by a double-screw kneader (HAAKE MiniLab Rheomex CTW5, manufactured by Thermo Electron Corporation) and pelletized. The kneading temperature herein was set at 200° C. and the rotation speed was set at 60 rpm. The raw material was supplied from a supply port of the kneader and kneaded for 3 minutes.

[Preparation of Product by Injection Molding and Evaluation of Thermoplasticity]

A molded body having the following shape was formed from the resin pellets obtained above by using an injection molding machine (HAAKE MiniJet II, manufactured by Thermo Electron Corporation).

Size of the molded body: thickness: 2.4 mm, width: 12.4 mm, length: 80 mm

The molding was performed in the conditions: cylinder temperature of the molding machine: 220° C., temperature of a mold: 60° C., injection pressure: 1200 bar (120 MPa) for 5 seconds and holding pressure: 600 bar (60 MPa) for 20 seconds.

Moldability in the above, which is related to thermoplasticity, was evaluated in accordance with the following criteria.

Criteria for evaluation of thermoplasticity:

◯: Moldability is satisfactory

Δ: Moldability is unsatisfactory (voids, sinks, unfilled portions are found)

x: Molding cannot be made

[Measurement of Bending Strength and Elastic Modulus]

The molded bodies obtained in the above were subjected to a three-point bending test using INSTRON5567 universal testing machine manufactured by Instron and performed in the following conditions to measure bending strength and elastic modulus.

Bending test conditions: Distance between fulcrum points: 32 mm, test speed: 1 mm/minute

The data obtained were evaluated in accordance with the following criteria.

Criteria for evaluation of bending strength:

◯: 50 MPa or more

x: less than 50 MPa

Criteria for evaluation of bending elastic modulus:

◯: 1.5 GPa or more

x: less than 1.5 GPa

[Measurement of Izod Impact Strength]

The molded bodies obtained above were subjected to measurement of notch Izod impact strength performed in the conditions described in JIS K7110.

The data obtained were evaluated in accordance with the following criteria.

Criteria for evaluation of Izod impact strength:

◯: 5.0 kJ/m² or more

x: less than 5.0 kJ/m²

[Measurement of Water Absorption Rate]

Water absorption rate was measured in accordance with JIS K7209. More specifically, the weight increase rate of a molded body when a molded body was soaked in pure water of normal temperature for 24 hours was measured.

The data obtained were evaluated in accordance with the following criteria for water resistance.

Criteria for evaluation of water resistance:

◯: less than 2.0%

x: 2.0% or more

[Determination of Plant-Derived Component Ratio]

Provided that the cellulose component and long-chain component (derived from stearic acid) were plant components, the total content (% by mass) of the plant components relative to the whole sample was obtained. The cellulose component herein corresponds to a structure represented by the above expression (1) where a hydroxy group neither acylated nor grafted; whereas the long-chain component corresponds to a partial structure of a fatty acid deficient in the terminal hydroxy group.

[Measurement of Main-Chain Crystallinity]

Main-chain crystallinity of the cellulose resin obtained was evaluated by X-ray diffractometry. As an X-ray diffractometer, X'Pert Pro manufactured by PANalytical was used. As an X-ray, CuKα ray was used. The cellulose resin was pressed at 200° C. and 100 kgf/cm² (9.8 MPa) in the form of film and then subjected to measurement. Alternatively, the cellulose resin (solid mass) recovered after synthesis was directly subjected to measurement.

The measurement results were evaluated for main-chain crystallinity in accordance with the following criteria.

Criteria for evaluation of crystallinity:

◯: (main-chain crystal is present): peak is found in the vicinity of either one or both of 2θ=22°, 34°

x: (main-chain crystal is not present): no peaks above are found

The cellulose resin evaluated as “main-chain crystal is present”, can be determined to have a reinforcing crystal structure due to the cellulose main-chain crystal.

[Evaluation of Solvent Resistance]

The cellulose resin obtained (0.1 g) was dispersed in chloroform (2 ml). Based on the behavior, solvent resistance was evaluated in accordance with the following criteria.

Criteria for evaluation of solvent resistance:

◯: not completely dissolved (swollen)

x: completely dissolved

(Example A2) (Cellulose Propionate Stearate)

A cellulose resin (cellulose propionate stearate) (13.3 g (yield 96%)) was obtained in accordance with the same quantity and method as in Example A1 except that the amount of starting propionyl chloride was changed to 10.28 g (111 mmol).

The sample (cellulose propionate stearate) obtained was subjected to measurement by ¹H-NMR in the same manner as in Example A1. As a result, DS_(Lo) was 0.30 and DS_(Sh) was 2.37.

This sample was evaluated in the same manner as in Example A1. The results are shown in Table 1.

(Example A3) (Cellulose Propionate Stearate)

A cellulose resin (cellulose propionate stearate) (14.5 g (yield 98%)) was obtained in accordance with the same quantity and method as in Example A1 except that the amount of starting stearoyl chloride was changed to 7.85 g (26 mmol) and the amount of starting propionyl chloride was changed to 10.28 g (111 mmol).

The sample (cellulose propionate stearate) obtained was subjected to measurement by ¹H-NMR in the same manner as in Example A1. As a result, DS_(Lo) was 0.39 and DS_(Sh) was 2.36.

This sample was evaluated in the same manner as in Example A1. The results are shown in Table 1.

(Example B1) (Cellulose Acetate Stearate)

After an activation treatment was applied to a cellulose, the cellulose was acylated in a solid-liquid heterogeneous system to obtain a cellulose resin. More specifically, the cellulose resin was prepared as follows.

First, the activation treatment of a cellulose was performed as follows.

Six grams (in terms of dry weight, 37 mmol/glucose unit) of cellulose (derived from a broad-leaf tree, pre-hydrolyzed craft pulp, water content: 8.3%) was cut into pieces having a several cm in size and dispersed in pure water (90 ml). After the dispersion solution was stirred for one hour, the content of liquid therein was reduced to 60% or less by suction filtration and squeeze. The cellulose was dispersed in 90 ml of acetic acid. The dispersion solution was subjected to the same stirring and liquid-removing steps as above and again dispersed in 90 ml of acetic acid. The dispersion solution was stirred, and liquid was removed from the solution to obtain activated cellulose.

Next, a mixed acid anhydride was prepared for acylation in accordance with the following method.

To a reactor purged with nitrogen, stearic acid (94.7 g (333 mmol)) and acetic anhydride (21.0 ml (222 mmol)) were placed. The mixture was stirred for one hour while heating at 100° C. to obtain a mixed acid anhydride. To this, dioxane (150 ml) was added and the mixture was kept warm at 50° C.

Next, a cellulose resin was synthesized in accordance with the following method.

The activated cellulose obtained above was placed in a reactor purged with nitrogen and dispersed in 400 ml of dioxane. The mixture was kept warm at 50° C. To this, the mixed acid anhydride-dioxane solution obtained above was added and further a solution, which was obtained by mixing concentrated sulfuric acid (0.33 ml) with dioxane (50 ml), was added. The reaction solution was stirred for 3 hours while heating at 50° C. After acylation was performed in this manner, pure water (5 ml) was added. The reaction solution was stirred at 60° C. for 2 hours and aging was performed.

Thereafter, to the solution aged, a water/methanol solution mixture (water: 50 ml, methanol: 2 L) was added to precipitate a product, which was recovered by suction filtration. The solid content obtained was washed three times with 200 ml of isopropanol at 60° C., rinsed with methanol and dried at 105° C. for 5 hours in vacuum to obtain a granule-like product.

The product obtained was dispersed in 400 ml of pure water and boiled at 100° C. for 2.5 hours. Subsequently, magnesium acetate (0.13 g) was added to the solution, which was boiled for 2 hours. Further, magnesium acetate (1.8 g) was added and the solution was boiled for 0.5 hours to remove the residual sulfate. A solid content was recovered by suction filtration, rinsed with methanol and dried at 105° C. for 5 hours in vacuum to obtain a powdery cellulose resin (cellulose acetate stearate) (9.9 g (yield 85%)).

The sample (cellulose acetate stearate) obtained was subjected to measurement by ¹H-NMR in the same manner as in Example A1. As a result, DS_(Lo) was 0.27 and DS_(Sh) was 1.97.

This sample was evaluated in the same manner as in Example A1. The results are shown in Table 1.

(Example B2) (Cellulose Acetate Stearate)

A cellulose resin (cellulose acetate stearate) (10.5 g (yield 85%)) was obtained in accordance with the same quantity and method as in Example B1 except that the time for aging the solution after adding pure water (5 ml) was changed to one hour.

The sample (cellulose acetate stearate) obtained was subjected to measurement by ¹H-NMR in the same manner as in Example A1. As a result, DS_(Lo) was 0.28 and DS_(Sh) was 2.27.

This sample was evaluated in the same manner as in Example A1. The results are shown in Table 1.

(Example C1) (Cellulose Acetate Stearate)

After an activation treatment was applied to a cellulose, the cellulose was acylated in a homogeneous solution system to obtain a cellulose resin. More specifically, the cellulose resin was prepared as follows.

First, the activation treatment of a cellulose was performed as follows.

Six grams (in terms of dry weight, 37 mmol/glucose unit) of cellulose (KC flock, W-50 GK manufactured in Nippon Paper, water content: 6.8%) was dispersed in 90 ml of pure water. The dispersion solution was stirred for one hour, subjected to suction filtration to reduce a liquid content to 60% or less, and dispersed in 90 ml of N,N-dimethylacetamide. In the same manner as the above, the dispersion solution was stirred, and liquid was removed from the solution to obtain activated cellulose.

Next, a mixed acid anhydride was prepared for acylation in accordance with the following method.

To a reactor purged with nitrogen, stearic acid (31.6 g (111 mmol)) and acetic anhydride (21.0 ml (222 mmol)) were placed. The mixture was stirred for one hour while heating at 100° C. to obtain a mixed acid anhydride. To this, N,N-dimethylacetamide (150 ml) was added and the mixture was kept warm at 70° C.

Next, a cellulose resin was synthesized in accordance with the following method.

The activated cellulose obtained above was placed in a reactor purged with nitrogen and dispersed in 180 ml of N,N-dimethylacetamide. The mixture was stirred for one hour. To this, lithium chloride (15.5 g) was added and the solution was stirred for 1.5 hours while heating at 100° C., and then, stirred overnight while cooling to room temperature. In this manner, the cellulose was completely dissolved. The solution was kept warm at 50° C. and a solution, which was obtained by dissolving dimethylamino pyridine (3.0 g) in N,N-dimethylacetamide (120 ml), was slowly added dropwise. The solution was further diluted with N,N-dimethylacetamide (150 ml) and the whole solution was kept warm at 70° C. To this, the mixed acid anhydride-N,N-dimethylacetamide solution obtained above was added and stirred for 6 hours while heating at 100° C. In this manner, acylation was performed.

Thereafter, methanol (2.5 L) was added to precipitate a product, which was recovered by suction filtration.

The solid content obtained was washed three times with 400 ml of isopropanol at 60° C., rinsed with methanol and dried at 105° C. for 5 hours in vacuum to obtain 12.0 g (yield 86%) of a powdery cellulose resin (cellulose acetate stearate).

The sample (cellulose acetate stearate) obtained was subjected to measurement by ¹H-NMR in the same manner as in Example A1. As a result, DS_(Lo) was 0.40 and DS_(Sh) was 2.60.

This sample was evaluated in the same manner as in Example A1. The results are shown in Table 1.

(Comparative Example A1) (Cellulose Propionate Stearate)

A cellulose resin (cellulose propionate stearate) (15.6 g (yield 87%)) was obtained in accordance with the same quantity and method as in Example A1 except that the amount of starting stearoyl chloride was changed to 11.2 g (37 mmol); and the amount of starting propionyl chloride was changed to 10.28 g (111 mmol).

The sample (cellulose propionate stearate) obtained was subjected to measurement by ¹H-NMR in the same manner as in Example A1. As a result, DS_(Lo) was 0.79 and DS_(Sh) was 2.02.

This sample was evaluated in the same manner as in Example A1. The results are shown in Table 1.

(Comparative Example B1) (Cellulose Acetate)

Cellulose acetate (product name: L-40) manufactured by DAICEL was directly used. Measurement by ¹H-NMR was performed in the same manner as in Example A1. As a result, DS_(Sh) was 2.45.

This sample was subjected to evaluation which was performed in the same manner as in Example A1. However, the sample was not molded because thermoplasticity was poor, with the result that strength and water absorption rate were not evaluated. The results are shown in Table 1.

(Comparative Example B2) (Cellulose Acetate Propionate)

Cellulose acetate propionate (product name: CAP482-20) manufactured by Eastman Chemical Company was directly used. Measurement by ¹H-NMR was performed in the same manner as in Example A1. As a result, DS_(Sh) was 2.83 (total of an acetyl group and a propionyl group)

This sample was evaluated in the same manner as in Example A1. The results are shown in Table 1.

(Comparative Example B3) (Cellulose Acetate Stearate)

After an activation treatment was applied to a cellulose, the cellulose was acylated in a solid-liquid heterogeneous system to obtain a cellulose resin. More specifically, the cellulose resin was prepared as follows.

First, the activation treatment of a cellulose was performed as follows.

Six grams (in terms of dry weight, 37 mmol/glucose unit) of cellulose (derived from a broad-leaf tree, pre-hydrolyzed craft pulp, water content: 8.3%) was cut into pieces having a several cm in size and dispersed in pure water (90 ml). After the dispersion solution was stirred for one hour, the content of liquid therein was reduced to 60% or less by suction filtration and squeeze. The cellulose was dispersed in 90 ml of acetic acid. The dispersion solution was subjected to the same stirring and liquid-removing steps as above and again dispersed in 90 ml of acetic acid. The dispersion solution was stirred, and liquid was removed from the solution to obtain activated cellulose.

Next, a mixed acid anhydride was prepared for acylation in accordance with the following method.

To a reactor purged with nitrogen, stearic acid (189.4 g (666 mmol)) and acetic anhydride (21.0 ml (222 mmol)) were placed. The mixture was stirred for one hour while heating at 100° C. to obtain a mixed acid anhydride. To this, dioxane (100 ml) was added and the mixture was kept warm at 50° C.

Next, a cellulose resin was synthesized in accordance with the following method.

The activated cellulose obtained above was placed in a reactor purged with nitrogen, dispersed in 150 ml of dioxane and kept warm at 50° C. To this, the mixed acid anhydride-dioxane solution mentioned above was added and a solution, which was obtained by mixing perchloric acid (0.12 ml) with dioxane (50 ml), was further added. The reaction solution was stirred for 4 hours while heating at 50° C. In this manner, acylation was performed.

Thereafter, a water/methanol solution mixture (water: 50 ml, methanol: 2 L) was added to precipitate a product, which was recovered by suction filtration. The solid content obtained was washed three times with 200 ml of isopropanol at 60° C., rinsed with methanol and dried at 105° C. for 5 hours in vacuum to obtain a powdery cellulose resin ((cellulose acetate stearate) 7.8 g (yield 74%)).

The sample (cellulose acetate stearate) obtained was subjected to measurement by ¹H-NMR in the same manner as in Example A1. As a result, DS_(Lo) was 0.12 and DS_(Sh) was 2.20.

This sample was subjected to evaluation which was performed in the same manner as in Example A1. However, the sample cannot be molded because thermoplasticity was poor, with the result that strength and water absorption rate were not evaluated. The results are shown in Table 1.

(Comparative Example C1) (Cellulose Acetate Stearate)

A cellulose resin (cellulose propionate stearate) (14.9 g (yield 90%)) was obtained in accordance with the same quantity and method as in Example C1 except that the amount of starting stearic acid was changed to 63.2 g (222 mmol).

The sample (cellulose propionate stearate) obtained was subjected to measurement by ¹H-NMR in the same manner as in Example A1. As a result, DS_(Lo) was 0.68 and DS_(Sh) was 2.32.

This sample was evaluated in the same manner as in Example A1. The results are shown in Table 1.

(Comparative Example C2) (Cellulose Acetate Stearate)

A cellulose resin (cellulose propionate stearate) (17.0 g (yield 86%)) was obtained in accordance with the same quantity and method as in Example C1 except that the amount of starting stearic acid was changed to 126.3 g (444 mmol).

The sample (cellulose propionate stearate) obtained was subjected to measurement by ¹H-NMR in the same manner as in Example A1. As a result, DS_(Lo) was 1.11 and DS_(Sh) was 1.89.

This sample was evaluated in the same manner as in Example A1. The results are shown in Table 1.

Table 1 summarizes the long-chain components, short-chain components and substitution degree and evaluation results of the cellulose resins produced. In the table, “C18” represents an octadecanoyl group (corresponding to the acyl group moiety contained in stearic acid), “C2” represents an acetyl group and “C3” represents a propionyl group.

TABLE 1 Long- Short- Plant- chain chain Water Heat derived Sol- compo- compo- Bending Elastic Impact absorp- resis- Thermo- component vent nent nent DS_(LO) + DS_(SH)/ strength modulus strength tion rate tance Tg plas- ratio Crystal- resis- (DS_(LO)) (DS_(SH)) DS_(SH) DS_(LO) [MPa] [GPa] [kJ/m²] [%] [° C.] ticity [%] linity tance Example A1 C18 C3 2.55 9.6 74 2.3 7.9 1.2 — ◯ 63 ◯ ◯ (0.24) (2.31) ◯ ◯ ◯ ◯ Example A2 C18 C3 2.67 7.9 77 2.4 5.5 1.0 — ◯ 64 ◯ ◯ (0.30) (2.37) ◯ ◯ ◯ ◯ Example A3 C18 C3 2.75 6.1 61 1.7 7.3  0.86 — ◯ 66 ◯ ◯ (0.39) (2.36) ◯ ◯ ◯ ◯ Example B1 C18 C2 2.24 7.3 93 2.3 6.5 1.9 — ◯ 73 X X (0.27) (1.97) ◯ ◯ ◯ ◯ Example B2 C18 C2 2.55 8.1 93 2.1 6.7 1.6 155 ◯ 71 X X (0.28) (2.27) ◯ ◯ ◯ ◯ Example C1 C18 C2 3.00 6.5 86 2.2 5.9 1.2 — ◯ 70 X X (0.40) (2.60) ◯ ◯ ◯ ◯ Comparative C18 C3 2.81 2.6 40 1.0 8.9  0.69 — ◯ 77 ◯ ◯ Example A1 (0.79) (2.02) X X ◯ ◯ Comparative — C2 2.45 ∞ — — — — — X 60 X X Example B1 (0)   (2.45) X X X X Comparative — C2 + C3 2.83 ∞ 97 2.3 3.7 3.1 — ◯ 50 X X Example B2 (0)   (2.83) ◯ ◯ X X Comparative C18 C2 2.32 18.3  — — — — — Δ 67 ◯ ◯ Example B3 (0.12) (2.20) X X X X Comparative C18 C2 3.00 3.4 44 1.1 8.0 0.7 — ◯ 77 X X Example C1 (0.68) (2.32) X X ◯ ◯ Comparative C18 C2 3.00 1.7 23 0.5 30   0.4 — ◯ 85 X X Example C2 (1.11) (1.89) X X ◯ ◯

As shown in Table 1, it is found that the cellulose resins of Examples according to an exemplary embodiment all have high plant-derived component ratio, thermoplasticity, excellent mechanical characteristics (bending strength, elastic modulus, impact strength) and durability (particularly water resistance and heat resistance). It is also found that the cellulose resins of Examples A1 to A3 having crystallinity are also excellent in solvent resistance.

In contrast, it is found that the cellulose resins of Comparative Examples which fail to satisfy the expression (2) are inferior in mechanical characteristics. In particular, the cellulose resins of Comparative Examples A1, C1 and C2, which give small values as the ratio given by the expression (2) (the ratio of a short-chain component is low, and the ratio of a long-chain component is large), are inferior in bending strength and elastic modulus. Conversely, it is found that the cellulose resins, which give large values as the ratio given by the expression (2) (a short-chain component alone is present, or the ratio of a short-chain component is large and the ratio of a long-chain component is small), are low in thermoplasticity (Comparative Examples B1, B3); whereas, in the cellulose resin (Comparative Example B2), even if thermoplasticity is present, the impact strength and water resistance are poor.

Having thus described the present invention with reference to the exemplary embodiments and Examples, the present invention is not limited to the above-described exemplary embodiments and Examples. Various modifications understandable to those skilled in the art may be made to the constitution and details of the present invention within the scope thereof.

This application claims the right of priority based on Japanese Patent Application No. 2015-256792 filed Dec. 28, 2015, the entire content of which are incorporated herein by reference. 

The invention claimed is:
 1. A cellulose resin formed by substituting hydrogen atoms of hydroxy groups of a cellulose with a long-chain component being a linear saturated aliphatic acyl group having 14 or more carbon atoms and a short-chain component, wherein the short-chain component is a propionyl group, the cellulose resin has a reinforcing crystal structure due to a cellulose main-chain crystal of the cellulose, and a degree of substitution with the long-chain component (DS_(Lo)) and a degree of substitution with the short-chain component (DS_(Sh)) satisfy conditional expressions (1) and (2) shown below: DS_(Lo)+DS_(Sh)≥2.1  (1) 4≤DS_(Sh)/DS_(Lo)≤12  (2).
 2. The cellulose resin according to claim 1, wherein the long-chain component is an acyl group moiety of at least one fatty acid selected from myristic acid, palmitic acid, stearic acid, arachidic acid and behenic acid.
 3. A molding material comprising the cellulose resin according to claim
 1. 4. A molded body formed by using the molding material according to claim
 3. 5. A process for producing the cellulose resin according to claim 1, comprising: acylating hydroxy groups of a cellulose constituting pulp by reacting the pulp dispersed in an organic solvent with a short-chain reactant selected from the group consisting of propionic anhydride and propionyl chloride, and a long-chain reactant being an acid chloride of a long-chain fatty acid and having the long-chain component, in the presence of an acid trapping component while warming; and separating an acylated cellulose obtained in the acylating from the organic solvent.
 6. The process for producing the cellulose resin according to claim 5, wherein the organic solvent is a solvent providing a liquid holding rate by cellulose of 90% by volume or more.
 7. The process for producing the cellulose resin according to claim 5, wherein the acid trapping component contains triethylamine or pyridine.
 8. The process for producing the cellulose resin according to claim 5, wherein the acylating is carried out at a reaction temperature of 50 to 100° C.
 9. The process for producing the cellulose resin according to claim 5, wherein the organic solvent is used in an amount 10 to 50 times as large as the dry mass of the pulp.
 10. The process for producing the cellulose resin according to claim 5, further comprising, after the acylating, a holding step at 25 to 75° C. for 1 to 5 hours after an aqueous alkaline solution is added.
 11. The cellulose resin according to claim 1, wherein DS_(Lo) is 0.2 or more, and DS_(Sh) is 1.7 or more.
 12. The cellulose resin according to claim 1, wherein DS_(Lo) is in a range of 0.2 to 0.6, and DS_(Sh) is in a range of 1.7 to 2.8.
 13. The cellulose resin according to claim 1, wherein in X-ray diffraction using CuKα, a peak is present in the vicinity of either one or both of 2 θ=22°, 34°.
 14. The cellulose resin according to claim 1, wherein a polymerization degree of the cellulose is in a range of 50 to
 5000. 